目的 贵州省某养殖场仔猪疑似感染PCV4，为了解该毒株的分子生物学特征。 方法 从疑似仔猪多系统衰竭综合征（PMWS）的病料中提取核酸，应用PCR方法进行PCV4 Cap基因全长扩增和测序。同时，运用生物信息学软件进行Cap基因和对其编码的氨基进行分析。 结果 所获得的PCV4 Cap核苷酸序列全长为687 bp，通过预测，在转录过程中，其起始密码子和终止密码子对应的DNA序列分别为ATG和TAA；核苷酸与参考毒株的同源性均在96.2%～99.1%，所编码氨基酸的相似性为89.5%～96.1%；ORF2编码的氨基酸变异位点共23个，且变异位点主要集中于115位之后；本试验所收集的19株PCV4 Cap基因系统进化树未呈现出空间和时间上的规律。 结论 在贵州省某养殖场发生断奶疑似仔猪多系统衰竭综合征的病料中检测到PCV4，该毒株的Cap基因与中国江西的JXYC-2021遗传距离较近，且从系统进化树上发现PCV4在全世界的分布无地域性。

Objectives The characteristic of molecular biology in one strain of Porcine Circovirus Type-4 suspected to be infected by piglets in a farm in Guizhou Province was studied. Methods Nucleic acids were extracted from the piglet multiple system failure syndrome (PMWS)-suspected piglets and PCR method was used to amplify and sequence the full-length of Cap gene in PCV4. Bioinformatics software was used to analyze the Cap gene and its encoded amino acids. Results The nucleotide sequence of Cap gene in PCV4 obtained was 687 bp in length. The DNA sequence corresponding to the start codon and stop codon during transcription was predicted to be ATG and TAA. The homology of nucleotides with the reference strain ranged from 96.2% to 99.1%, and the similarity of encoded amino acids ranged from 89.5% to 96.1%. There was a total of 23 amino acid mutated sites encoded by ORF2, and the mutation sites were mainly concentrated after position 115. The 19 phylogenetic trees of Cap gene in PCV4 collected in this experiment had no spatial and temporal pattern. Conclusions One strain of PCV4 was detected in a suspected piglet with PMWS in a farm in Guizhou Province. The Cap gene of this strain is genetically close to JXYC-2021 in Jiangxi, China, and it was found from the phylogenetic tree that PCV4 has no regional distribution worldwide.